Random technology proliferation. If lots of people are ahead of you in a tech it increases the chance that the tech “leaks” to you. The % of remaining players ahead of you could increase the chance while the amount they’re ahead could increase the number of levels you get. This could be done without adding new techs, just the new mechanic for them to spread.

Purposeful espionage. You could build spies of some sort that are only effective (or much more effective) against larger empires. The mechanic could be the same as the first idea, but instead of random chance, you’d have to build the spies and send them at empires. Basically similar to spies in Civ.

I kind of like the first because it’s automatic (although leaves you at the mercy of random number generators.)

Either way, I think just catching you up in tech if you manage to hang on is the most natural mechanic, though perhaps not as effective in the end as giving you special access to some tech purpose-built to get you back in the game.

Seems reasonable to me, but might make games drag on a bit? It’d depend on how expensive you made the spies.

Perhaps the mechanism could be that each spy/level of spy you build would ‘attack’ another (neighboring?) player’s technology each tick or update. If that tech was bigger than yours, then you’d steal a level of it (so L4 vs L7 means that you go to L5). This way spies would benefit players who are behind, and be pretty useless if you were ahead, with diminishing returns in between.